Method of working aluminum



Patented Jan. 29, 1935 UNITED STATES PATENT orrlcr.

Aluminum Company Pa., a corporation of of America, Pittsburgh, Pennsylvania No Drawing. Application April 6, 1933 Serial No. 664,774

3 Claims.

This invention relates to processes of upsetting wire, rod, bar, or similar shapes of heattreatable aluminum base alloys, and to the solution of the peculiar problems incident thereto.

While the invention will be described with direct mention to the manufacture of rivets from rod or wire, it is generally applicable to those processes by which at least one end of a rod, bar, or wire or similarly shaped metal product is .0 worked by forging, pressing, upsetting or the like to flow a portion of the metal outwardly and to thus form on the metal shape an enlarged portion or head. It is this general class of processes of which the manufacture of rivets is a typical [5 and common example. The words rod or wire will be used herein and in the appended claims to generally denote those metal shapes of large or small size which are exemplified by rod, bar,

or wire, and the process of enlarging at least to one end of such shapes will hereinafter be generally termed upsetting. fers to the process of upsetting rod or wire made of heat-treatable aluminum base alloy, which latter term comprehends the large and well known 25 class of aluminum base alloy possessed of latent strength, ductility, elasticity, and similar properties which are increased and developed under the influence of the solution heat-treatments well known to the art. Such solution heat- 30 treatments comprise heating the alloy to those temperatures at which a substantial proportion of the soluble alloying elements present therein form solid solutions with the aluminum, and then cooling the alloy to retain in an unstable 35 condition of equilibrium the solid solutions thus formed. Ancillary to such solid solution treatments are the low temperature treatments designed to, partially at least, correct said unstable condition of equilibrium after it is once obtained. 40 Such heat-treatable aluminum base alloys form a distinct and recognized general class and are well exemplified by the aluminum base alloys which contain alloying elements such as copper, magnesium, zinc, silicon and the like which are 45 capable of forming solid solutions with aluminum.

In the art of forming rivets from heat-treatable aluminum base alloys, the rod or wire is produced from such alloys by drawing or like processes of working. This working imparts to 60 the metal such internal stresses and such hardness properties that it usually is not immediately subjected to the upsetting process designed to form the head of the rivet as the severe work additionally induced into the metal by the upll setting overworks the metal and causes metal The invention re--- failures such as are usually evidenced by cracks in the formed rivet head. It is therefore usually desirable to anneal the metal prior to the upsetting operation; i. e., to submit the rod or wire, prior to ,the upsetting process, to such a heating 5 process as will remove from the metal a substantial proportion of the hardness and internal strains induced therein by the process by which the metal was worked into the shape of rod or wire but which will not harden the-metal. The rod or wire, once annealed, if necessary, and the hardness and internal strains induced by working substantially removed, is then subjected to the upsetting process, and the rivet head, or similarly enlarged portion, is formed on at least one 16 end thereof. These operations completed, it is then necessary to heat-treat the rivet to develop in the heat-treatable aluminum base alloy of which it is made the latent properties of tensile strength and hardness usually necessary to the 20 application of the rivet. It will be noted, of course, that such heat-treatments must, commercially, take place after the forming of the rivet head because of the fact that if the metal is heat-treated prior to the upsetting operation, it is usually hardened to such an extent as to preclude satisfactory operation of the upsetting process.

In practicing such processes as the rivet-making process above described, it has been observed that the completed and heat-treated rivet is not regularly of good quality and is oftentimes coarse- 1y crystalline or of irregular crystal size. This condition is deleterious in any metal product which must withstand strains or tension in use, and it is particularlydisadvantageous where, as in the case of rivets, a part of the product is again worked to form, as in the usual riveting practice, another head or enlarged portion on the rod or wire, because the head or enlarged portion 40 so formed tends to belumpy and uneven and to contain evidences of metal failure such as shear cracks.

' It is, therefore, desirable to devise a process of upsetting heat-treatable aluminum base alloy rod or bar to produce a final headed product which will. after solution heat-treatment, be structurally composed of fine and uniform size crystals.

The invention is predicated upon the discovery that the stated object may be obtained if the rod or wire, after the annealing treatment but prior to the upsetting operation, is subjected to an amount of cold working necessary to reduce the cross-sectional area of the worked object by at least 20 per cent but less than that amount of cold working which would so harden the metal as to defeat the purpose of the previous annealing treatment and preclude the successive upsetting of the metal. This cold working may ordinarily be achieved by drawing the wire or by similarly working the metal in the cold. While the exact amount of cold working which should not be exceeded in order to obtain the best results will vary according to the particular heat-treatable aluminum base alloy in use, this optimum amount can readily be ascertained by experiment. It is a general rule, however, that cold working should not exceed that amount necessary to reduce the cross-sectional area of the metal objectby 50 per cent. The term annealing as used in this application denotes a condition in the metal where substantially all of the hardness imparted to the metal by previous working is removed by heattreatment at a temperature which in practice usually lies above the recrystallization temperature of the metal or alloy. Therefore, although an annealing step is mentioned as a part of the invention herein described, it will be immediately apparent that where the metal has been originally worked prior to cold working at a temperature above the recrystallization temperature so that no substantial amount of strain hardening or work hardness has been imparted to the metal, that metal is equivalent to metal which is in the annealed condition, and the steps of cold working herein described will, when imposed upon such metal, produce the results of the present invention.

The invention, therefore, contemplates the addition to the known processes of making rivetshaped objects from heat-treatable aluminum base alloy rod or wire, of the further intermediate step of working subsequent to the annealing operation but prior to the upsetting operation. Consequently the process of the invention comprises the following successive steps; to wit:

(a) Annealing previously worked heat-treatable aluminum base alloy rod or wire to remove therefrom a substantial proportion of the hardness imparted to the metal by the previous working.

(b) Cold working the annealed rod or wire to reduce its cross-sectional area by at least 20 per cent but less than about 50 per cent (1. e., less than that amount of cold working which would preclude a subsequent and successful upsetting operation).

(c) Subjecting the annealed and cold worked rod or wire to an upsetting process to form an enlarged portion on at least one end thereof.

By the practice of methods comprising these steps, it is possible to commercially produce an average product which after solution heat-treatment will be found to have a physical structure composed of comparatively fine and uniform crystals as compared with the coarse and nonuniform crystal structure so often produced in the aluminum base alloy product of the prior processes.

Although the process of the invention has been described with reference to three steps. it will be noted that the essence thereof is the cold working, prior to upsetting, of heat-treatable aluminum base alloy rodor wire which is annealed, i. e., which is substantially free from internal strains or hardness induced by working or any other process, such as heat-treatment, which will induce such hardness.

I claim:

1. The method of working heat-treatable aluminum base alloy wire or rod from which internal strains and hardness have been removed by annealing, comprising cold working the annealed wire or rod to reduce its cross-sectional area by at least about 20 per cent but less than about 50 per cent, and thereafter subjecting the wire or rod to an upsetting process.

2. The method of working heat-treatable aluminum base alloy wire or rod comprising annealing the previously worked wire or rod to remove therefrom a substantial proportion of the hardness induced by said working, cold working the annealed wire or rod to reduce its cross-sectional area by at least about 20 per cent but less than about 50 per cent,.and thereafter subjecting the -wire or rod to an upsetting process.

3. The method of working heat-treatable aluminum base alloy wire or rod which is free from substantial amounts of internal strains and hardness comprising cold working the wire or rod to reduce its cross-sectional area by at least 20 per cent but less than 50 per cent, and thereafter subjecting the wire or rod to an upsetting process.

HENRY D. MONSCH. 

